The operational use of the gas chambers in Auschwitz was preceded by experiments intended to find the most effective chemical agent and to work out the proper method for its use. About 600 Soviet POWs and 250 sick Poles were killed in such experimentation from September 3-5, 1941. Afterwards, the morgue at crematorium I in the main camp was adapted for use as a gas chamber. Several hundred people at a time could be killed in this room.
The provisional gas chambers
In the spring of 1942, a second gas chamber went into operation in a specially adapted farmhouse whose owner had been expelled. The house stood outside the fence of the Birkenau camp, which was then under construction. Camp commandant Rudolf Höss and Adolf Eichmann, the Reich Main Security Office representative in charge of deportation to extermination center, chose this house together during a visit by Eichmann.
The adaptation work involved partially walling up the windows and reconfiguring the interior. According to Höss, about 800 people at a time could be killed in the house. Two barracks for undressing were erected nearby. This gas chamber was withdrawn from service in the spring of 1943, after the entry into use of the new gas chambers at crematoria II-V.
A second house belonging to a farmer who had been expelled, and also standing outside the Birkenau camp fence, was adapted as a gas chamber in mid-1942. Höss estimated that 1,200 people at a time could be killed in this house. Three barracks for undressing were erected nearby. This gas chamber was also withdrawn from use in the spring of 1943. It was put back into use in the spring of 1944, at the time of the extermination of the Hungarian Jews.
The four large gas chambers and crematoria
The construction of 4 large gas chambers and crematoria began in Birkenau in 1942. They went into operation between March 22 and June 25-26, 1943. The gas chambers at crematoria II and III, like the undressing rooms, were located underground, while those at crematoria IV and V stood at ground level. About 2 thousand people at a time could be put to death in each of them. According to calculations made by the Zentralbauleitung on June 28, 1943, the crematoria could burn 4,416 corpses per day—1,440 each in crematoria II and III, and 768 each in crematoria IV and V. This meant that the crematoria could burn over 1.6 million corpses per year. Prisoners assigned to do the burning stated that the daily capacity of the four crematoria in Birkenau was higher—about 8 thousand corpses.
The construction of another facility according to a new design, crematorium VI, never progressed beyond the planning stage.
Murdering people in the gas chambers
In principle, all Jews classified because of their age or physical condition as unfit for labor were subject to immediate extermination directly after their arrival in the camp, without being registered or assigned a number.
In addition to the Jews, a certain number of Soviet POWs, estimated by witnesses as several thousand men, were killed with gas. A certain number of Poles were also killed in the gas chamber. The first group of prisoners selected and killed in a gas chamber outside the camp, at the Sonnenstein euthanasia center, consisted mostly of Poles. Cases are also known of the killing in the gas chambers of groups of Poles selected in the so-called camp hospital, numbering up to several hundred at a time, or as a punishment for the revolt of the penal company, or sentenced to death by the summary court. Several thousand Gypsies also died in the gas chambers. Prisoners of other nationalities also died during the period, from mid-1941 to the spring of 1943, when selection took place in the camp, usually in the blocks for the sick.